HOLD BRAKE FEATURE FAILED, VEHICLE ROLLED CAUSING A COLLISION. VEHICLE WAS STATIONARY AND RUNNING ON A CITY STREET, HOLD WAS ENGAGED AND WHEN DRIVER DOOR WAS OPENED THE PARKING BRAKE INDICATOR ILLUMINATED. AFTER STEPPING OUT AND CLOSING THE DRIVER DOOR, VEHICLE BRAKE DISENGAGED AND VEHICLE BEGAN MOVING RESULTING IN CRASH WHILE UNOCCUPIED.